1. Field of the Invention
The present invention relates generally to data processing, and more particularly but not exclusively to techniques for combating spam.
2. Description of the Background Art
Electronic mail (“e-mail”) has become a relatively common means of communication among individuals with access to a computer network, such as the Internet. Among its advantages, e-mail is relatively convenient, fast, and cost-effective compared to traditional mail. It is thus no surprise that a lot of businesses and home computer users have some form of e-mail access. Unfortunately, the features that make e-mail popular also lead to its abuse. Specifically, unscrupulous advertisers, also known as “spammers,” have resorted to mass e-mailings of advertisements over the Internet. These mass e-mails, which are also referred to as “spam e-mails” or simply “spam,” are sent to computer users regardless of whether they asked for them or not. Spam includes any unsolicited e-mail, not just advertisements. Spam is not only a nuisance, but also poses an economic burden.
Various anti-spam techniques have been developed to combat spam. In a content-level anti-spam, the content of each received e-mail is scanned for words, phrases, and other characteristics indicative of spam. Although content-level anti-spam has been proven effective, it doesn't do anything to reduce network traffic. This is primarily because an e-mail must be received by the anti-spam application at the destination network to be scanned in the first place. In connection-level anti-spam, the anti-spam application connects to a network reputation service (NRS) to check the reputation of the sender of the received e-mail. The network reputation service maintains a database of known spammers. The network reputation service compares the sender information of the received e-mail with those of known spammers to determine whether or not the received e-mail is spam. While connection-level anti-spam reduces network traffic to some extent, it still needs to accept a connection from a spammer, determine the reputation of the spammer, and then close the connection. Therefore, even in connection-level anti-spam, spammers still generate a substantial amount of network traffic.